Create page providers for JBPM tasks and processes

Creating a page provider will make it possible to use content views for tasks and processes display on the new JSF dashboard, as well as the new Opensocial dashboard.

Page providers will need the following features:

• be able to retrieve some user tasks, with some configuration options to define (include or not isolated tasks with no process, for instance)
• be able to retrieve some user processes

This page provider will not handle sort nor pagination for now, as additional things need to be taken care of:

• if the document linked to the task/process does not exist anymore, or is in the trash, or is not accessible for current user, task/process should not be displayed
• ideally some generic methods should be added to the JbpmService interface for it